The invention of living carbocationic polymerizations, specifically that of isobutylene, was a milestone in synthetic polymer science because, in addition to a synthetic breakthrough, it lead to the development of several commercially significant products. One of these products is telechelic polyisobutylene (F-PIB-F, where F=functional group, PIB=polyisobutylene), the enabling intermediate of poly(styrene-b-isobutylene-b-styrene) (SIBS), the drug eluting coating on Boston Scientific's Taxus® coronary stent implanted in and enhancing the quality of life of millions of people!
A cost analysis of the product revealed that up to 90% of the cost of the commercially significant low molecular weight (defined herein as Mn˜3000 g/mol or less) telechelic polyisobutylene is due to the “blocked” initiator 1,3(2-methoxy-2-propyl)-5-tert butylbenzene (hereinafter “tBuDiCumMeO”) employed for its synthesis. The reasons for using this specific structure are well known, but to date, no other structures have been commercially available and/or commercially successful for the specific use as a polymerization initiator for the specific living carbocationic polymerizations desired.
In fact, heretofore, only one other attempt, (see Applicants' of record co-pending PCT Application No. PCT/US11/68104) has been known to have been made to produce other polymerization initiators that are far less expensive and just as efficient as the initiator, tBuDiCumMeO. However, even that relatively new synthesis of, for example, 1,3-di(2-methoxy-2-propyl)-5-isopropyl benzene (also noted sometimes hereinafter as “iPrDiCum MeO”), is believed to be far more expensive than necessary, and more expensive that the synthesized compounds provided in this disclosure. This is because, in order to use an isopropyl group-containing initiator rather than tert-butyl group-containing initiator, the new isopropyl group-containing initiator would require FDA approval as a polyisobutylene(PIB)-based biomaterial. Under FDA guidelines, the isopropyl group initiator residue contained in the PIB would need to be tested and approved before use as a biomaterial. The high cost of testing to obtain FDA approval of the isopropyl group-containing initiator could be problematic to its commercial success in the growing industry of initiators for carbocationic polymerizations.
Thus, a need still exists for a simple low cost synthesis for other polymerization initiators, particularly those containing a tert-butyl residues, which will not require FDA approval. Given the relative expense in the preparation and use of tBuDiCumMeO initiators for the production of telechelic polyisobutylenes, and the fact that isopropyl group-containing initiators must still obtain FDA approval, the need continues to exist for methods of synthesizing other functionally efficient, low cost initiators containing tert-butyl residues, whether well-known or not.